Hi, I have a PDB file which I have trimmed such that it contains only two residues, say residue-10 and residue-25 (I have given the numbers to denote that the residues are far apart from each other in the primary structure of the protein) and saved as a new PDB file. In order to prevent formation of any pseudobonds between the two residues, I manually added a TER row in the PDB file, just after the entry of the last atom of residue-10. Now, when I delete all the atoms of residue-10 except the atoms of its carbonyl group i.e., its backbone C-atom and covalently linked backbone O-atom and run the "addh" command, chimera adds H-atoms to the relevant atoms of residue-25 but doesn't adds H-atoms to the C-atom of residue-10 due to which its valency remains incomplete. Can you please tell me why it is happening? Is there any way to overcome this problem? -- Prathvi Singh, Research Fellow, Department of Biological Sciences & Bioengineering, Indian Institute of Technology, Kanpur-208016